1. Technical Field
The present invention relates generally to electronic imaging technology and, more particularly, to a one-dimensional microwave or millimeter wave image scanning apparatus. The apparatus of the present invention is especially well-suited for geographic imaging applications such as generating real-time video pictures of a landing strip for an airplane or of the surface of the ocean in search of oil contamination.
2. Discussion
Various types of imaging systems have been developed for use in conjunction with geographic imaging applications, with radar systems being one of the most popular. Radar and similar imaging technologies operate by transmitting a radiowave signal towards a target and then detecting a return signal reflected back from the target. The return signals and the rate at which they return are used to generate information about the target and its location. These systems, however, innately experience difficulties in attaining geographic images in various adverse environmental conditions such as snow, rain, dust or fog.
Utilizing millimeter wave or microwave energy has provided a viable alternative and presents various advantages over use of other signal types. As microwave or millimeter wave energy is naturally present in the environment and is reflected to some degree off of most objects, it is possible to obtain a video image or picture passively, without having to transmit an excitation signal and without necessitating a return signal response. Also, microwave or millimeter wave energy is not substantially attenuated by atmospheric moisture such as fog, snow or rain and millimeter waves penetrate adverse environmental conditions such as smoke and dust clouds wherein suspended particles are of less than a millimeter in size. Due to shorter wavelengths, millimeter wave systems can be physically implemented with relatively small antennas, useful in applications where small antennas are particularly advantageous such as on an airplane.
Such millimeter wave imaging devices conventionally employ a two dimensional focal plane array wherein a lens or other focusing element is used to focus millimeter wave radiation obtained from the field of view onto the array. Each focal plane element in the array receives a microwave signal and converts the radiation incident thereon into an electrical output signal used to drive a video display of the image. Each output signal generated by an array element is most often mapped to one image element.
With such conventional systems, however, the resulting video picture produced may appear ragged or coarse due to discrete pixelization and image undersampling. Each pixel of the displayed image represents radiation from the portion of the image radiated in a direction directly incident on a given detector. Since there are practical physical limitations on the number of and spacing between focal plane elements in the array structure, some of the image information may be lost, especially that not corresponding to a central portion of a detector element. This not only causes greatly degraded image quality but also leads to the exclusion of many image enhancement techniques. More accurate information would be obtainable if some of the direct radiation corresponding to peripheral regions of the detector could be directed toward the center. While various mechanical scanning methods have been used to alleviate such difficulties, the speed at which the mechanical scanner has to operate limits the practical application of such techniques.
In view of the above, there is a need for an improved imaging system which utilizes energy in the millimeter wave or microwave spectrum to produce a refined high quality video picture for which various image enhancement techniques are available. It is also desirable that such systems have no mechanical moving parts to reduce overall system complexity and to improve reliability.